Generally, an undergraduate degree requires you study what other people already know. A graduate degree, especially a PHD requires you to develop techniques for creating new knowledge. A Master's degree is somewhat between a Bachelor's and a PHD; you learn some research techniques and enhance your mastery of a given subject, but aren't required to make a fundamental advance in your field. Bachelor's degrees include a general eduction requirement, while graduated degrees are solely focused on a particular subject. There are also some professionally oriented graduate degrees for business, law, Medicine, etc. These professions require more than a bachelor's level of competence before one can become a practitioner, or as in the case of an MBA, open some opportunities that wouldn't be available otherwise.